1. Field of the Invention
This invention relates to a structure and a method for differentiating one object from another, and in particular to a structure which optically detects weeds and then eliminates those weeds.
2. Description of Related Art
In many situations it is necessary to distinguish one type of object from another. While this is essential in such diverse areas as manufacturing, data processing and mail delivery, object differentiation is particularly important in agriculture. For example, the ability to distinguish weeds from desired plants is essential to allow weeds to be destroyed because even sparse weed populations decrease the moisture, light and nutrients available to crop plants, thereby significantly reducing yields of these crops. Additionally, weeds can clog machinery and impede access to crops during farm operations such as harvesting. Spraying of herbicide is a conventional method of controlling weeds. However, when spraying herbicide to control scattered weeds, most of the herbicide is wasted by being deposited on bare soil where the herbicide has no effect. Because herbicides are expensive, many growers attempt to save money by using less herbicide. However, larger chemically-tolerant weeds often escape control because of insufficient herbicide application. Moreover, herbicides may have highly undesirable effects on the environment, for example, by causing contamination of ground water or causing chemical burning of different crops in adjacent fields during floods. Thus, a need exists to reduce both herbicide cost and environmental impact by selectively spraying only the weeds.
Methods for optically distinguishing between soil and plants are currently known in the art. However, many of these methods use devices which rely on natural sunlight to create a reflected image. Thus, the devices cannot operate at night, and are seriously impaired under cloudy conditions, or even when operated in shadows. Other methods for optically distinguishing between soil and plants use devices which rely on an artificial white light source to create the reflected image. However, under normal (i.e. sunny) operating conditions, this artificial light source must compete with the sun which is thousands of times brighter and constantly changing in brightness and spectral distribution. Therefore, either method, i.e. using natural sunlight or an artificial white light source, fails to reliably provide an accurate wavelength signature of objects in the field of view of the device sufficient to eliminate individual weeds. Indeed, applications for these methods have been limited to weed control of low-till or no-till field crops where this lack of precision can be tolerated. However, orchards, vineyards, and row crops require a high degree of accuracy in weed control. Thus, a need exists for a device which provides accurate optical sensing of the weeds and efficient elimination of those weeds.